Having the widget on the main index.php page would increase both visibility and usage of the app since I'm assuming the majority of visitors don't actually click through to the comments page unless the article requires a "read more" link.

In a related note, if the widget were to be placed on the main index.php page, it might make sense to offer multiple templates -- e.g. a vertically-oriented widget to be placed in a sidebar. Also, a more compact version of the widget would be nice since it would likely be repeated on the same page several times.